1. Field of the Invention
This invention relates to a method for measuring the parameter of a rough film, and more particularly, to a method of monitoring the manufacturing process of rough film by using a measuring light with wavelength in a certain range and a spectroscopic ellipsometer (SEM) as the measuring instrument.
2. Description of the Prior Art
Currently, with the giant advancement in semiconductor technology, the integration density of the integrated circuits has been tremendously increased. Generally speaking, the enhancement in the integration density of the integrated circuits requires a corresponding improvement in their manufacturing process. For example, the capacitor in a dynamic random access memory (DRAM) has to provide a higher capacitance without reducing the integration density. However, the diminution of capacitance will result from the decrease of capacitor surface area when the device area gets smaller. Therefore, other ways of manufacturing DRAM are necessary to increase the capacitance efficiently but still meet the requirements of a smaller device area. This will result in a few obvious benefits, such as the efficient increase of DRAM refresh time and, power saving due to the lowering of memory consuming power. On the contrary, if the capacitance fails to be increased, the refresh time of memory can't be increased efficiently either, then data access will be degraded.
In general, a roughening technique, that is, increasing the capacitor surface-area is used to enhance the capacitance of a capacitor in the integrated circuits, which is the main technology to make stack DRAMs and is called hemispherical grain silicon (HSG). The cross-sectional view of the process diagram is shown in FIG. 1, in which amorphous silicon 10 in a device is fonned as a rough film 15 (hemispherical grain) after annealing according to the prior art. However, though the HSG technique can enhance capacitance effectively, monitoring the process is difficult and controlling roughness with good quality control of HSG stability in manufacturing process is almost impossible.
In another aspect, although the technique of selective HSG has dominated the methods of fonning stack DRAM, due to the special structure of hemi-spherical grain, there is a need to provide a cheap in-line control method when applying this technique. If in-line scanning electron microscopy (SEM) is used as the inspecting tool, the problems are high cost, limited throughput, and the biggest-good control of process stability. Because it is very subjective and hard to make a judgment whether the manufacturing process is good or bad under scanning electron microscopy, thus SPC control will be very difficult. Besides, general optical methods have the following restrictions:
1. Microscopic roughness and non-homogeneous make it inefficient to get the optical property of films by optical measurement. PA1 2. Because HSG, that is, a rough film is fonned by crystal growth, the properties of amorphous silicon, such as the refractive coefficient, the extinction coefficient, and the thickness of bottom layer will directly disturb the correct measurement. So, all the disturbances have to be removed first to make the measurement indicative of the property of a rough film.
Therefore, a convenient and simple way to measure the parameter of a rough film is necessary to be developed that the influence from the bottom layer can be got rid of and moreover, the property of the rough film can be accurately measured.